Wireless Local Area Network (WLAN) offers wireless broadband service, including VoIP and other data services, in a small area with limited mobility. WLAN, especially in terms of Wi-Fi (802.11a/b/g), is been widely deployed in many places. Wireless Wide Area Network (WWAN) offers voice and/or data services over a large geographical area with true mobility. Some device manufacturers are developing or have developed multi-mode terminal devices that are able to work in WLAN and WWAN.
However, the multi-mode devices typically cannot or do not operate in multiple modes (both WLAN and WWAN) simultaneously due to technical difficulties, cost, battery drain, and so forth. For example, if the terminal is working in WLAN mode, then the WWAN circuit may be shut down which makes the terminal unavailable in WWAN.
In addition, typical multi-mode terminal devices have unique directory numbers in different access networks. For example, a terminal may have a directory number in the corporate environment (for example, PBX or PABX) and a directory number in the WWAN network. The problem of ensuring that a call to the terminal's number in an access network reaches the terminal that is currently in a different access network requires a solution.
Current solutions in the industry focus on new functional nodes and signaling protocols in the network to handle the call routing based on the presence of the mobile terminal. This approach requires new network nodes and protocols to be implemented by the network service providers in the current networks, which can be costly, technically difficult, and problematically places the burden of the solution on the service provider.